The present invention relates to medical devices, and particularly to expandable medical devices such as cannulas, catheters, retractors, and similar devices.
Existing cannulas as used in endoscopic surgery today are passive devices which are fixed in length and width. They can not be varied intraoperatively in length and width to accommodate larger devices or varying size devices through the skin.
Skin and subcutaneous (subsurface) tissues are viscoelastic: they will gradually stretch without tearing. Once the tissue is slowly stretched it maintains its expanded condition for a period of time. Alternatively, the tissue can be stretched further, for example to progressively stretch out an incision. Then, after relaxation, the tissue will regain its original unstretched condition without having been damaged.